1. Field of the Invention
The present invention relates to a high pressure pump.
2. Description of Related Art
A fuel supply apparatus, which supplies fuel to an internal combustion engine, includes a high pressure pump, a fuel rail and fuel injection valves. The high pressure pump pumps high pressure fuel. The fuel rail accumulates the high pressure fuel, which is pumped from the high pressure pump. The fuel injection valves are connected to the fuel rail and inject the high pressure fuel received from the fuel rail. The pressure of the fuel rail may possible exceed its allowable range due to, for example, malfunction of an intake valve or a discharge valve of the high pressure pump or abnormal temperature increase, thereby resulting in an abnormally high pressure of the fuel rail. In order to address such a disadvantage, a previously proposed high pressure pump includes a relief valve that relieves, i.e., releases an excessively high pressure, which is equal to or higher than a predetermined relief pressure, to a return passage, so that damage of, for example, the fuel injection valve(s) can be limited.
When the engine is stopped, circulation of the engine coolant is stopped. This results in an increase in the temperature of the engine room. In response to the increase in the temperature of the engine room, the pressure of the fuel rail is increased, so that fuel may possibly leak from the fuel injection valves. Furthermore, when the temperature of the fuel in the fuel rail is increased beyond the evaporating temperature of the fuel, fuel vapor may possibly be generated in the fuel rail. When the generated vapor is accumulated in the fuel rail or is injected from the fuel injection valves along with the fuel, the startability of the engine may possibly be deteriorated.
In view of the above disadvantage, JP2010-48259A teaches a high pressure fuel supply apparatus, which includes a check valve in a relief valve. This check valve opens when the pressure of fuel in the fuel rail is larger than a predetermined pressure to enable flow of fuel from the fuel rail to a discharge valve located on an upstream side of the fuel rail. The predetermined pressure is set such that the amount of fuel leaked from the fuel injection valve upon the engine stop becomes smaller than its allowable amount, and the amount of vapor generated in the fuel rail upon the engine stop becomes smaller than its allowable amount.
With the technique of JP2010-48259A, it is possible to reduce the required installation space by placing the check valve in the relief valve. However, according to this technique, the check valve and the relief valve are separately formed. Therefore, a valve element and a valve seat of each of the check valve and the relief valve need to be accurately formed to a level that ensures fluid tightness between the valve element and the valve seat. Therefore, the number of processing steps and the processing costs may possibly be increased.